This project uses a process (U.S. Patents 3,928,584 & 3,932,628 assigned to NIH) to obtain sap in quantity from trees. Extracts obtained by evaporating the sap at 100 degrees C have yielded an exceptionally large number showing confirmed activity against P388(lymphocytic leukemia). Sap extracts from 544 North American tree species yielded 38 (7%) with confirmed activity against this cancer. From 1499 species from Costa Rica 177 (12%) showed confirmed activity. Extracts prepared by conventional methods from roots, bark, wood, leaves, flowers and fruits of these same tree species have yielded only about 1% confirmed actives. The work is continuing with Peruvian species.